schema: space upgrade fixes

 - Add func_id_by_name to box.internal. It will be used in EE.
 - Don't call box.internal.space.upgrade from box.schema.space.upgrade -
   we will redefine box.schema.space.upgrade in EE instead.

Follow-up commit 38b25832 ("box: add space upgrade stubs").

NO_DOC=internal
NO_TEST=internal
NO_CHANGELOG=internal